Ion mobility spectrometers (IMS) are widely used in field chemical analysis. IMS separate ionic species based on their ion mobility in a given media (either gas or liquid). Recent development of the IMS technology results in two forms of IMS instruments and systems. The time-of-flight (TOF) IMS separate ions based on their steady state ion mobilities under constant electric field. High resolving power with IMS has been achieved with the TOF-IMS instruments. Alternatively, devices that separate ions based their mobility changes under high field conditions, such as field asymmetric ion mobility spectrometer (FAIMS) or differential mobility spectrometer (DMS), can also be used. These devices separate the ions through the use of nonlinear mobility, which occurs at high values of normalized electric field (E/n). The normalized electric field refers to the relation between the applied electric field at a given location in space divided by the neutral particle number density. The normalized electric field is a key parameter in ionized gases and plasmas, as the energy of ionized particles, the breakdown and sustaining voltages and other key parameters depend upon this ratio. The FAIMS and/or DMS devices have sensitivity and selectivity that are still substantially worse (less) than linear drift tubes.
In many cases, in a less-than ideal operating environments (in particular those with high humidity or other site-specific interferences), the spectrometer performance is significantly limited. The performance of the ion mobility spectrometers in these circumstances can be improved by increasing the temperature of the gas. High temperature ion mobility spectrometers are common in applications that require high resolution analysis, such as explosive detection. Unfortunately, the use of high temperature drift tubes in IMS devices results in high power consumption, limited portability and other operational disadvantages, including slow turn-on from cold conditions. In addition, dry drift gas is often required in these spectrometers. A dehumidifier in front of the unit has been used to address these problems (either as a water absorber or as a hydrophobic membrane) with significant trade-offs. The volume and weight, as well as the need for regeneration, makes the use of dehumifier cell impractical, while the use of the hydrophobic membrane decreases the volume/amount of the sample that is introduced into the device, decreasing its sensitivity.